1. Field of the Invention
The present invention relates to spinal disc prostheses to replace a damaged, degenerated or otherwise defective spinal disc in a spinal column of a human.
2. Background
The prior art is replete with various types of prosthetic or artificial spinal discs designed to replicate a spinal disc and thus replace a damaged, degenerated or otherwise defective spinal disc in a spinal column of a human. U.S. Pat. Nos. 5,071,437 and 5,534,030 disclose spinal disc prostheses that are typical of the prior art. The discs disclosed in these US patents include a pair of rigid plates adhered to opposite surfaces of a body of elastomeric material. Many other variations have since been developed.
The disc prosthesis when in use is positioned between adjacent vertebrae. The rigid plates may have bone in-growth material for enabling bone to adhere or fuse to the rigid plates. The disc prosthesis is subject to forces that act in the spine including compression forces due to loads on the spine, shear forces due to bending of the spine, and torsion forces due to twisting of the spine. These application forces may cause disc component failure. For example, such application forces may cause the rigid plates to separate from the body of elastomeric material in the disc prostheses of the '437 and '030 patents. Such separation would be detrimental to the proper functioning of the disc prosthesis. Moreover, these application forces have a tendency to squeeze the elastomeric body out from between the two plates. This, again, is detrimental to the proper functioning of the disc prosthesis.
When a visco-elastic material is used for the prosthetic disc body between two plates, the application forces and their attendant problems are especially true. Particularly, such spine application forces can compress a portion or more of a visco-elastic spinal disc prosthesis body from between the two plates thereof. Moreover, the application forces tend to rotate the disc body. Excess rotation can cause stress on the disc body. Such stress can lead to disc body failure in all types of prior art discs.
It is apparent from the above that prior art spinal disc prostheses fall short of providing a reliable artificial disc.
In view of the above, it is desirable to provide spinal disc prostheses that alleviate the shortcomings of the prior art.